In general, for the purposes of the present disclosure the definition “pipeline” means a pipeline, which, in use, lies on the bed of a body of water or is partially buried in the bed of the body of water and is intended to convey gases and/or liquids, in particular hydrocarbons. A pipeline of the type identified above can extend for hundreds of kilometers, comprises sections of pipeline joined to each other aboard a vessel, and launched into the body of water from the vessel, and is laid on the bed of the body of water by the advancement of the vessel. Generally, each section of pipeline has a length of 12 meters, a relatively large diameter of between 0.2 and 1.5 meters, and comprises a steel cylinder; a protective coating, which is made of polymeric material, is placed in contact with the steel cylinder and protects the steel cylinder from corrosion; and sometimes a weighing coat of concrete or gunite is placed in contact with the protective coating. The pipelines are usually buried in the bed near the docks and in shallow waters to protect underwater pipelines from hydrodynamic stress, from temperature fluctuations, and from possible contact with foreign bodies which could jeopardize the integrity of said pipelines, including ice in extreme weather conditions. The burying of pipelines in the bed of the body of water or their covering by appropriate-sized rocky material is a widespread practice in shallow water, but is relatively hard to execute and economically unsustainable in deep waters, where the risk profile for exposed pipes may be considered acceptable in first analysis. As a result, underwater pipelines placed on the bed of a body of water in deep water may be exposed to blunt objects such as containers falling from ships in transit or accidentally pulled behind the respective craft, literally “ploughing” the bed of the body of water and possibly damaging the pipeline by lacerating the pipeline. The frequency of these incidents is relatively low, but the damage caused is relatively very high both in terms of the environmental damage which ensues, and in terms of the fact that the energy supply of many countries is closely related to the transport of hydrocarbons through underwater pipelines of the type identified above. As a result, when these incidents happen, action must be taken relatively quickly to repair the pipeline and restore the hydraulic seal and mechanical characteristics of the same.
Methods have been proposed for such purpose which provide for carrying out all the repair phases in the body of water, and other methods which provide for performing certain repair phases above the body of water and other repair phases in the body of water. One repair method described in the U.S. Pat. No. 5,437,517 comprises steps of cutting a length of underwater pipeline containing the damaged area to define a first and a second section of underwater pipeline having respectively a first and a second end; joining a first coupling head to the first section of underwater pipeline in the body of water; joining a second coupling head to the second section of underwater pipeline in the body of water; laying a telescopic sleeve with a third and a fourth coupling head in the body of water and placing the telescopic sleeve between the first and second coupling head; aligning the first section of underwater pipeline, the second section of underwater pipeline and the telescopic sleeve in the body of water; adjusting the length of the telescopic sleeve in the body of water; joining the telescopic sleeve to the first and second coupling head in the body of water. Subsequently, the telescopic sleeve is locked into the final position. All the above operations are performed in the body of water using scuba equipment controlled by remote-controlled underwater vehicles (ROV: Remotely Operated Vehicle) connected to a vessel via a cord (umbilical).
Other methods described in documents European Patent No. 2,430,346 and European Patent No. 2,430,347 are based on the use of telescopic sleeves and permit the repair of pipelines or merely the joining of sections of pipeline laid separately. Telescopic sleeves or other types of compensation sleeves create weakened zones of the pipeline and increase the number of operations to be performed and the complexity of the join. Still other complex methods for joining pipeline sections are disclosed in PCT Patent Application No. WO 03/040602, Great Britain Patent No. 2,038,973, and French Patent No. 2,928,987.